DOCSLIB.ORG

Volatiles, Geodynamics and Solid Earth Controls on the Habitable Planet 1. Introduction

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Volatiles, Geodynamics and Solid Earth Controls on the Habitable Planet 1. Introduction Volatiles, Geodynamics and Solid Earth Controls on the Habitable Planet The Earth is a layered, planetary body from the core to the atmosphere, with mantle, lithosphere and hydrosphere between. Water and gas are in abundance on the fertile surface we inhabit that overlies the barren, tracts of solid silicate mantle. This familiar arrangement has fundamentally compartmentalised the study of the Earth, with the hot interior frequently assumed to be dry. Such thinking has been reinforced by the practical difficulties of measuring the low abundances of volatiles within the Earth. Yet it has become increasingly apparent that the small amounts of volatile constituents can have a dominant effect on the behaviour of the mantle. As the largest reservoir on Earth, even small abundances of volatiles in the mantle can represent a major inventory of the planet’s volatiles. Thus the influence of volatile species on the operation of the mantle, which controls the storage and release of these volatiles to the surface represents Earth System Science on the grandest, most challenging scale. Advances in measurements of volatiles in nature and experiments, an understanding of their effects on rheology and an ability to compute these effects on the dynamics of the Earth now converge for the community to address this inter-connected system holistically. This Research Theme will thus quantitatively move geological thinking from a largely separate dry interior and wet exterior to a fully interacting model of the Earth. We will address the critical state of balance of the planet. Under what range of starting conditions can the Earth evolve to a planet with oceans and plate tectonics, and how robust is this system to perturbations? Can we lose our oceans and greenhouse-regulated atmosphere to the interior just as readily as we seem to have acquired them? Not only is the time ripe to tackle these zeroth order problems but there are the critical density of skills within the UK Geoscience community in order to efficiently address the interlinked components in this truly inter-disciplinary endeavour. 1. Introduction melts that produce continental crust would not Interactions between the mantle and the Earth's form. surface have dominated the evolution of the crust, • Carbonate sediment recycling back into the the oceans, and the atmosphere and those same mantle (via subduction) followed by emission processes control many aspects of the habitable via volcanic degassing is part of a long-term environment. The mantle is, by many orders of feedback modulating atmospheric CO2 levels magnitude, the largest reservoir of many volatiles that has been increasingly important since ~ on Earth (e.g., H2O, C, N, S), and volcanic 200 Ma – how was CO cycled in the Earth degassing and subduction ‘ingassing’ play a major 2 role in their cycles. The input and output of before this time? volatiles at plate boundaries provide major links • The link between mantle redox evolution and in the cycles of many important elements, large changes in surface chemistry, leads to including oceanic nutrients and climate-mediating major transitions such as the rise of species. Processes occurring at plate-boundaries atmospheric oxygen at 2.5 Ga and the underlie the generation of many mineral, transition from "iron rich, stagnant and low hydrocarbon, and geothermal resources, and play an important role in most volcanic and seismic oxygen" (ferruginous/euxinic) waters to hazards. Feedbacks among the mantle, the "oxygenated oceans" (oxic) oceans at ~0.5 lithosphere, the cryosphere, the hydrosphere, and Ga. the atmosphere exert long-term controls on Despite the planet’s self-regulation during many climate and the biosphere. Examples include: carbon-driven ‘hyperthermal’ crises in the past, it • By modulating mantle rheology, partial is unlikely to do so fast enough for humankind melting and redox state, volatiles influence given our current anthropogenic rates of carbon the operation and style of mantle convection release to the atmosphere. An improved and plate tectonics (perhaps even playing a understanding of the role of volatiles in geodynamics, and especially the sensitive crucial role in its initiation). connections between the deep Earth, habitability • The composition of magmas at subduction and the environment, is a vital component of our zones and ultimately the composition of the knowledge, both as an intellectual endeavour and continental crust depends on volatile budgets. in terms of managing our future relationship with Without water the silica-rich low density our planet. 1 2. The Research Programme (RP) The and been influenced by, redox (reduction- proposed RP, Volatiles, Geodynamics and Solid oxidation) reactions through geological time? Earth Controls on the Habitable Planet, will 3) How have the content and distribution of focus on the fundamental science of volatiles and volatiles influenced mantle convection and deep Earth processes, plate tectonics, melting and plate tectonics since the Earth formed? volcanism and their feedbacks to the surface Some of the key interplays relevant to these environment. This action specifically addresses themes are summarised in Figure 1. The scope ESS Theme Challenge 2: Understanding the long and delivery of each of these high-level themes is term development of the Earth and its addressed in turn in the following sections. 1 habitability which, amongst its goals, seeks to 3.1 How has cycling of volatiles between the “Improve knowledge and understanding of: how Earth’s surface and interior influenced the deep-earth processes influence the surface evolution of the habitable planet? environment; and the controls on subduction and mantle convection, melting and volcanism.” The importance of the mantle in determining the The goal of this RP is to understand the dynamic role of volatiles in mediating fundamental Earth processes that affect habitability, including mantle convection, plate tectonics, mantle melting and magma delivery, geohazards, and geothermal and ore-forming systems. Specifically the RP will aim to define and understand the controls on the volatile flows and budgets in the mantle, and their feedbacks with mantle behaviour, through well- defined programmes including observations on active geological systems (subduction zones, mantle plumes and spreading centres) and palaeo- analogues, together with closely-aligned laboratory experiments and computer simulations, and coupled geodynamic modelling and seismic imaging. It is expected that successful bids to this Figure 1. Schematic summary of volatile cycling programme will combine scientists from a wide and influences – which should be considered in the range of sub-disciplines within Earth Sciences, critical context of time, since the magnitude and and that their chosen areas of study will be type of influence will have varied over the 4.5 Ga of justified on the grounds of the relevance of those Earth history. areas to global Earth System Science problems. It ability of the planetary surface to support life is through truly interdisciplinary work that depends on the mass and composition of volatiles innovation will come; the RP will act as a catalyst initially available in the mantle, and the exchange to initiate work between communities of scientists fluxes of volatiles into and out of the surface that do not necessarily traditionally work together. reservoirs. The interplay between the surface 3.The Science and Delivery reservoir and deep Earth volatile budgets has evolved over geological time. Thus our The programme will require a highly understanding of volatile cycling between the collaborative and interdisciplinary approach deep Earth and the surface breaks down into four involving expertise across a wide range of fields related questions: including geophysics, geochemistry, mineral physics and petrology, and involving fieldwork, (i) What was the Earth’s initial volatile laboratory studies and computer modelling. It is inventory? envisaged that the program will involve delivery Our understanding of the origin of volatiles within via competitive consortium-scale (or larger) the planet has evolved dramatically in the last few proposal(s) to address and integrate the following years, linking the origin of mantle volatiles to three interlinked major themes: those brought to the Earth trapped in meteorites2. 1) How has cycling of volatiles between the There is evidence from intraplate volcanic Earth’s surface and interior influenced the systems that the mantle also contains volatiles 3 evolution of the habitable planet? from the earliest Solar Nebula . These initial 2) How have volatile flows both within the solid volatiles have been complemented by recycled 4. Establishing the initial volatile Earth and its surface reservoirs controlled, surface volatiles 2 element inventory of the mantle provides a key wedge, triggering melting and emerging boundary condition for any assessment of the ultimately in arc magmas, while others are mantle volatile output to the surface. recycled into the mantle. The efficiency of Delivery: The grand challenge is to resolve the recycling and its long-term variability are different contributions to the major volatile unknown, but the extent to which volatiles are species from accretionary or recycled sources. released or retained by subducting slabs is thought This can now be done using and integrating key to be controlled primarily by the thermal structure 5 geochemical tracers such as noble gases, halogens of subduction zones . and incompatible
Load more

Recommended publications
  • Apatite from NWA 10153 and NWA 10645—The Key to Deciphering Magmatic and Fluid Evolution History in Nakhlites
    minerals Article Apatite from NWA 10153 and NWA 10645—The Key to Deciphering Magmatic and Fluid Evolution History in Nakhlites Łukasz Birski 1,*, Ewa Słaby 1, Elias Chatzitheodoridis 2, Richard Wirth 3, Katarzyna Majzner 4, Gabriela A. Kozub-Budzy ´n 5, Jiˇrí Sláma 6, Katarzyna Liszewska 1, Izabela Kocjan 7 and Anna Zagórska 7 1 Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Warsaw, Twarda 51/55, 00-818 Warsaw, Poland; [email protected] (E.S.); [email protected] (K.L.) 2 Department of Geological Sciences, School of Mining and Metallurgical Engineering, National Technical University of Athens, 9 Heroon Polytechneiou, 15780 Zografou, Athens, Greece; [email protected] 3 Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum GFZ, Telegrafenberg, 14473 Potsdam, Germany; [email protected] 4 Faculty of Chemistry, Jagiellonian University, Raman Imaging Group, Gronostajowa 2, 30-387 Cracow, Poland; [email protected] 5 Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, Mickiewicza 30, 30-059 Cracow, Poland; [email protected] 6 Institute of Geology Academy of Sciences of the Czech Republic Rozvojová 269, 165 00 Prague Czech Republic; [email protected] 7 Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Cracow, Senacka 1, 31-002 Cracow, Poland; [email protected] (I.K.); [email protected] (A.Z.) * Correspondence: [email protected] Received: 10 September 2019; Accepted: 7 November 2019; Published: 10 November 2019 Abstract: Apatites from Martian nakhlites NWA 10153 and NWA 10645 were used to obtain insight into their crystallization environment and the subsequent postcrystallization evolution path.
    [Show full text]
  • Constraints on the Depth and Thermal Vigor of Melting in the Martian Mantle
    PUBLICATIONS Journal of Geophysical Research: Planets RESEARCH ARTICLE Constraints on the depth and thermal vigor 10.1002/2014JE004745 of melting in the Martian mantle Key Points: Justin Filiberto1 and Rajdeep Dasgupta2 • Mantle potential temperature calculated for Gale Crater rocks 1Department of Geology, Southern Illinois University, Carbondale, Illinois, USA, 2Department of Earth Science, Rice • 1450 ± 70°C may represent global Noachian mantle temperature University, Houston, Texas, USA • Consistent with simple convective cooling of the interior of Mars Abstract Studies of rocks in Gale Crater and clasts within the Martian meteorite breccia Northwest Africa (NWA) 7034 (and paired stones) have expanded our knowledge of the diversity of igneous rocks that make up the Martian crust beyond those compositions exhibited in the meteorite collection or Correspondence to: J. Filiberto, analyzed at any other landing site. Therefore, the magmas that gave rise to these rocks may have been fi[email protected] generated at significantly different conditions in the Martian mantle than those derived from previously studied rocks. Here we build upon our previous models of basalt formation based on rocks analyzed in Citation: Gusev Crater and Meridiani Planum to the new models of basalt formation for compositions from Gale Filiberto, J., and R. Dasgupta (2015), Crater and a clast in meteorite NWA 7034. Estimates for the mantle potential temperature, TP based on Constraints on the depth and thermal vigor of melting in the Martian mantle, Noachian age rock analyses in Gale Crater, Gusev Crater, and Bounce Rock in Meridiani Planum, and a J. Geophys. Res. Planets, 120, vitrophyre clast in NWA 7034 are within error, which suggests that the calculated average TP of 1450 ± 70°C doi:10.1002/2014JE004745.
    [Show full text]
  • Effects of Water on Seismic Wave Velocities in the Upper Mantle Terior. Therefore, If One Understands the Relation Between Water
    No. 2] Proc. Japan Acad., 71, Ser. B (1995) 61 Effects of Water on Seismic Wave Velocities in the Upper Mantle By Shun-ichiro KARATO Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455 (Communicated by Yoshibumi ToMODA,M. J. A., Feb. 13, 1995) Abstract : Possible roles of water to affect seismic wave velocities in the upper mantle of the Earth are examined based on mineral physics observations. Three mechanisms are considered: (i) direct effects through the change in bond strength due to the presence of water, (ii) effects due to the enhanced anelastic relaxation and (iii) effects due to the change in preferred orientation of minerals. It is concluded that the first direct mechanism yields negligibly small effects for a reasonable range of water content in the upper mantle, but the latter two indirect effects involving the motion of crystalline defects can be significant. The enhanced anelastic relaxation will significantly (several %) reduce the seismic wave velocities. Based on the laboratory observations on dislocation mobility in olivine, a possible change in the dominant slip direction in olivine from [100] to [001] and a resultant change in seismic anisotropy is suggested at high water fugacities. Changes in seismic wave velocities due to water will be important, particularly in the wedge mantle above subducting oceanic lithosphere where water content is likely to be large. Key words : Water; seismic wave velocity; upper mantle; anelasticity; seismic anisotropy. Introduction. Water plays important roles in the terior. Therefore, if one understands the relation melting processes and hence resultant chemical evolu- between water content and seismic wave velocities, tion of the solid Earth.
    [Show full text]
  • Chapter 5: Shock Metamorphism and Impact Melting
    5. Shock Metamorphism and Impact Melting ❖❖❖ Shock-metamorphic products have become one of the diagnostic tools of impact cratering studies. They have become the main criteria used to identify structures of impact origin. They have also been used to map the distribution of shock-pressures throughout an impact target. The diverse styles of shock metamorphism include fracturing of crystals, formation of microcrystalline planes of glass through crystals, conversion of crystals to high-pressure polymorphs, conversion of crystals to glass without loss of textural integrity, conversion of crystals to melts that may or may not mix with melts from other crystals. Shock-metamorphism of target lithologies at the crater was first described by Barringer (1905, 1910) and Tilghman (1905), who recognized three different products. The first altered material they identified is rock flour, which they concluded was pulverized Coconino sandstone. Barringer observed that rock flour was composed of fragmented quartz crystals that were far smaller in size than the unaffected quartz grains in normal Coconino sandstone. Most of the pulverized silica he examined passed through a 200 mesh screen, indicating grain sizes <74 µm (0.074 mm), which is far smaller than the 0.2 mm average detrital grain size in normal Coconino (Table 2.1). Fairchild (1907) and Merrill (1908) also report a dramatic comminution of Coconino, although only 50% of Fairchild’s sample of rock flour passed through a 100 mesh screen, indicating grain sizes <149 µm. Heterogeneity of the rock flour is evident in areas where sandstone clasts survive within the rock flour. The rock flour is pervasive and a major component of the debris at the crater.
    [Show full text]
  • Geomagnetism and Paleomagnetism Membership Survey
    Membership Survey: Geomagnetism and Paleomagnetism (GP) Section What is your primary section or focus group affiliation? Response Answer Options Response Count Percent Geomagnetism and Paleomagnetism (GP) Section 71.0% 363 Study of Earths Deep Interior (SEDI) Focus Group 4.5% 23 Planetary Sciences (P) Section 2.0% 10 Tectonophysics (T) Section 7.0% 36 Near-Surface Geophysics (NS) Focus Group 5.1% 26 Other (please specify) 10.4% 53 answered question 511 skipped question 0 What is your primary section or focus group affiliation? Geomagnetism and Paleomagnetism (GP) Section Study of Earths Deep Interior (SEDI) Focus Group Planetary Sciences (P) Section Tectonophysics (T) Section Near-Surface Geophysics (NS) Focus Group Other (please specify) Membership Survey: Geomagnetism and Paleomagnetism (GP) Section What (if any) is your secondary affiliation? Response Answer Options Response Count Percent Geomagnetism and Paleomagntism Section 24.0% 121 Study of Earth's Deep Interior Focus Group 15.0% 76 Planetary Sciences Section 13.7% 69 Tetonophysics Section 22.8% 115 Near-Surface Geophysics Focus Group 10.7% 54 None 24.2% 122 answered question 505 skipped question 6 What (if any) is your secondary affiliation? 30.0% 25.0% 20.0% 15.0% 10.0% 5.0% 0.0% None and Section Section Geophysics FocusGroup Near-Surface Planetary Focus Group DeepInterior Tetonophysics Geomagnetism Paleomagntism Study of Earth's Study of SciencesSection Membership Survey: Geomagnetism and Paleomagnetism (GP) Section List additional secondary affiliations (if any): Answer Options
    [Show full text]
  • Earth, Environmental and Planetary Sciences 1
    Earth, Environmental and Planetary Sciences 1 MATH 0090 Introductory Calculus, Part I (or higher) Earth, Environmental PHYS 0050 Foundations of Mechanics (or higher) Nine Concentration courses and Planetary Sciences EEPS 0220 Earth Processes 1 EEPS 0230 Geochemistry: Earth and Planetary 1 Materials and Processes Chair EEPS 0240 Earth: Evolution of a Habitable Planet 1 Greg Hirth Select three of the following: 3 Students in Earth, Environmental, and Planetary Sciences develop a EEPS 1240 Stratigraphy and Sedimentation comprehensive grasp of principles as well as an ability to think critically EEPS 1410 Mineralogy and creatively. Formal instruction places an emphasis on fundamental EEPS 1420 Petrology principles, processes, and recent developments, using lecture, seminar, EEPS 1450 Structural Geology laboratory, colloquium, and field trip formats. Undergraduates as well as graduate students have opportunities to carry out research in current fields Two additional upper level EEPS courses or an approved 2 of interest. substitute such as a field course One additional upper level science or math course with approval 1 The principal research fields of the department are geochemistry, from the concentration advisor. mineral physics, igneous petrology; geophysics, structural geology, tectonophysics; environmental science, hydrology; paleoceanography, Total Credits 13 paleoclimatology, sedimentology; and planetary geosciences. Emphasis in these different areas varies, but includes experimental, theoretical, and Standard program for the Sc.B. degree observational approaches as well as applications to field problems. Field This program is recommended for students interested in graduate study studies of specific problems are encouraged rather than field mapping for and careers in the geosciences and related fields. its own sake. Interdisciplinary study with other departments and divisions is encouraged.
    [Show full text]
  • The Upper Mantle and Transition Zone
    The Upper Mantle and Transition Zone Daniel J. Frost* DOI: 10.2113/GSELEMENTS.4.3.171 he upper mantle is the source of almost all magmas. It contains major body wave velocity structure, such as PREM (preliminary reference transitions in rheological and thermal behaviour that control the character Earth model) (e.g. Dziewonski and Tof plate tectonics and the style of mantle dynamics. Essential parameters Anderson 1981). in any model to describe these phenomena are the mantle’s compositional The transition zone, between 410 and thermal structure. Most samples of the mantle come from the lithosphere. and 660 km, is an excellent region Although the composition of the underlying asthenospheric mantle can be to perform such a comparison estimated, this is made difficult by the fact that this part of the mantle partially because it is free of the complex thermal and chemical structure melts and differentiates before samples ever reach the surface. The composition imparted on the shallow mantle by and conditions in the mantle at depths significantly below the lithosphere must the lithosphere and melting be interpreted from geophysical observations combined with experimental processes. It contains a number of seismic discontinuities—sharp jumps data on mineral and rock properties. Fortunately, the transition zone, which in seismic velocity, that are gener- extends from approximately 410 to 660 km, has a number of characteristic ally accepted to arise from mineral globally observed seismic properties that should ultimately place essential phase transformations (Agee 1998). These discontinuities have certain constraints on the compositional and thermal state of the mantle. features that correlate directly with characteristics of the mineral trans- KEYWORDS: seismic discontinuity, phase transformation, pyrolite, wadsleyite, ringwoodite formations, such as the proportions of the transforming minerals and the temperature at the discontinu- INTRODUCTION ity.
    [Show full text]
  • Invited Review
    INVITED REVIEW Presolar grains from meteorites: Remnants from the early times of the solar system Katharina Lodders a,* and Sachiko Amari b a Planetary Chemistry Laboratory, Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, Campus Box 1169, One Brookings Drive, St. Louis, MO 63130, USA b Department of Physics and McDonnell Center for the Space Sciences, Washington University, Campus Box 1105, One Brookings Drive, St. Louis, MO 63130, USA Received 5 October 2004; accepted 4 January 2005 Abstract This review provides an introduction to presolar grains – preserved stardust from the interstellar molecular cloud from which our solar system formed – found in primitive meteorites. We describe the search for the presolar components, the currently known presolar mineral populations, and the chemical and isotopic characteristics of the grains and dust-forming stars to identify the grains’ most probable stellar sources. Keywords: Presolar grains; Interstellar dust; Asymptotic giant branch (AGB) stars; Novae; Supernovae; Nucleosynthesis; Isotopic ratios; Meteorites 1. Introduction The history of our solar system started with the gravitational collapse of an interstellar molecular cloud laden with gas and dust supplied from dying stars. The dust from this cloud is the topic of this review. A small fraction of this dust escaped destruction during the many processes that occurred after molecular cloud collapse about 4.55 Ga ago. We define presolar grains as stardust that formed in stellar outflows or ejecta and remained intact throughout its journey into the solar system where it was preserved in meteorites. The survival and presence of genuine stardust in meteorites was not expected in the early years of meteorite studies.
    [Show full text]
  • Metabolic Engineering of Plant Volatiles Natalia Dudareva1 and Eran Pichersky2
    COBIOT-516; NO OF PAGES 9 Available online at www.sciencedirect.com Metabolic engineering of plant volatiles Natalia Dudareva1 and Eran Pichersky2 Metabolic engineering of the volatile spectrum offers enormous Metabolic engineering requires a basic understanding of potential for plant improvement because of the great the biochemical pathways and the identification of the contribution of volatile secondary metabolites to reproduction, genes and enzymes involved in the synthesis of volatile defense and food quality. Recent advances in the identification compounds. In the last decade a renewed interest in these of the genes and enzymes responsible for the biosynthesis of questions combined with technical advances have led to volatile compounds have made this metabolic engineering both a large increase in the number of plant volatiles highly feasible. Notable successes have been reported in identified as well as remarkable progress in discovering enhancing plant defenses and improving scent and aroma the genes and enzymes of volatile biosynthesis. Numer- quality of flowers and fruits. These studies have also revealed ous attempts have been made to modulate volatile pro- challenges and limitations which will be likely surmounted as files in plants via metabolic engineering to enhance direct our understanding of plant volatile network improves. and indirect plant defense and to improve scent and Addresses aroma quality of flowers and fruits [2–5]. While a few 1 Department of Horticulture and Landscape Architecture, Purdue projects have been successful in achieving the desired University, West Lafayette, IN 47907, United States goals, many other attempts have resulted in meager 2 Department of Molecular, Cellular and Developmental Biology, University of Michigan, 830 North University Street, Ann Arbor, MI enhancement of volatiles or in other unpredicted meta- 48109, United States bolic consequences such as further metabolism of the intended end products or deleterious effects on plant Corresponding author: Dudareva, Natalia ([email protected]) growth and development.
    [Show full text]
  • Joint Mineral Physics and Seismic Wave Traveltime Analysis of Upper Mantle Temperature
    Joint mineral physics and seismic wave traveltime analysis of upper mantle temperature Jeroen Ritsema1, Paul Cupillard2, Benoit Tauzin3, Wenbo Xu1, Lars Stixrude4, Carolina Lithgow-Bertelloni4 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA 2Seismological Laboratory, University of California–Berkeley, Berkeley, California 94720, USA 3Ecole et Observatoire des Sciences de la Terre, Institut de Physique du Globe de Strasbourg, 67084 Strasbourg, France 4Department of Earth Sciences, University College London, London WC1E 6BT, UK ABSTRACT CONVERTED WAVE TRAVELTIMES We employ a new thermodynamic method for self-consistent Teleseismic P wave conversions, denoted as Pds, propagate as com- computation of compositional and thermal effects on phase transition pressional (P) waves through the deep mantle and convert to shear (S) depths, density, and seismic velocities. Using these profi les, we compare waves at an upper mantle discontinuity at depth d beneath the seismom- theoretical and observed differential traveltimes between P410s and eter. The phases P410s and P660s, for example, are waves that have P (T410) and between P600s and P410s (T660–410) that are affected only by converted from P to S at the 410 km and the 660 km transitions, respec- seismic structure in the upper mantle. The anticorrelation between T410 tively (Fig. 1). and T660–410 suggests that variations in T410 and T660–410 of ~8 s are due to Our data are recorded traveltime differences between the phases lateral temperature variations in the upper mantle transition zone of P410s and P (T410) and between P660s and P410s (T660–410). T410 and ~400 K. If the mantle is a mechanical mixture of basaltic and harzbur- T660–410 are unaffected by imprecise earthquake locations and lower mantle gitic components, our traveltime data suggest that the mantle has an hetero geneity.
    [Show full text]
  • The Nakhlite Meteorites: Augite-Rich Igneous Rocks from Mars ARTICLE
    ARTICLE IN PRESS Chemie der Erde 65 (2005) 203–270 www.elsevier.de/chemer INVITED REVIEW The nakhlite meteorites: Augite-rich igneous rocks from Mars Allan H. Treiman Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058-1113, USA Received 22 October 2004; accepted 18 January 2005 Abstract The seven nakhlite meteorites are augite-rich igneous rocks that formed in flows or shallow intrusions of basaltic magma on Mars. They consist of euhedral to subhedral crystals of augite and olivine (to 1 cm long) in fine-grained mesostases. The augite crystals have homogeneous cores of Mg0 ¼ 63% and rims that are normally zoned to iron enrichment. The core–rim zoning is cut by iron-enriched zones along fractures and is replaced locally by ferroan low-Ca pyroxene. The core compositions of the olivines vary inversely with the steepness of their rim zoning – sharp rim zoning goes with the most magnesian cores (Mg0 ¼ 42%), homogeneous olivines are the most ferroan. The olivine and augite crystals contain multiphase inclusions representing trapped magma. Among the olivine and augite crystals is mesostasis, composed principally of plagioclase and/or glass, with euhedra of titanomagnetite and many minor minerals. Olivine and mesostasis glass are partially replaced by veinlets and patches of iddingsite, a mixture of smectite clays, iron oxy-hydroxides and carbonate minerals. In the mesostasis are rare patches of a salt alteration assemblage: halite, siderite, and anhydrite/ gypsum. The nakhlites are little shocked, but have been affected chemically and biologically by their residence on Earth. Differences among the chemical compositions of the nakhlites can be ascribed mostly to different proportions of augite, olivine, and mesostasis.
    [Show full text]
  • Reviewing Martian Atmospheric Noble Gas Measurements: from Martian Meteorites to Mars Missions
    geosciences Review Reviewing Martian Atmospheric Noble Gas Measurements: From Martian Meteorites to Mars Missions Thomas Smith 1,* , P. M. Ranjith 1, Huaiyu He 1,2,3,* and Rixiang Zhu 1,2,3 1 State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, 19 Beitucheng Western Road, Box 9825, Beijing 100029, China; [email protected] (P.M.R.); [email protected] (R.Z.) 2 Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China 3 College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China * Correspondence: [email protected] (T.S.); [email protected] (H.H.) Received: 10 September 2020; Accepted: 4 November 2020; Published: 6 November 2020 Abstract: Martian meteorites are the only samples from Mars available for extensive studies in laboratories on Earth. Among the various unresolved science questions, the question of the Martian atmospheric composition, distribution, and evolution over geological time still is of high concern for the scientific community. Recent successful space missions to Mars have particularly strengthened our understanding of the loss of the primary Martian atmosphere. Noble gases are commonly used in geochemistry and cosmochemistry as tools to better unravel the properties or exchange mechanisms associated with different isotopic reservoirs in the Earth or in different planetary bodies. The relatively low abundance and chemical inertness of noble gases enable their distributions and, consequently, transfer mechanisms to be determined. In this review, we first summarize the various in situ and laboratory techniques on Mars and in Martian meteorites, respectively, for measuring noble gas abundances and isotopic ratios.
    [Show full text]